When completing a production or injection wellbore, casing can sometimes be installed to line the walls of the wellbore. Casing can include steel piping with an outer diameter that is less than the diameter of the wellbore. The casing can help provide structural support to the wellbore and seal the wellbore from parts of the geologic formation in which the wellbore has been formed.
Installing casing involves running long strings of pipe, also known as casing strings, through at least a portion of a wellbore, from a topside facility. While the casing string is being run, fluid can be circulated through the casing string and up through the annulus formed between the outer surface of the casing string and the inner wall of the wellbore. The circulating fluid helps provide static pressure on the geologic formation to prevent a “kick” from the wellbore, or releasing pressurized hydrocarbons to the environment.
Once the casing has reached a target depth within the wellbore, cement can be circulated similarly to the previously circulated fluid. The cement hardens in the annulus and secures the casing in place. The cement can also act as an added layer of protection between the wellbore and the geologic formation.